/Engine/Plugins/Runtime/GeometryCache/Source/GeometryCache/Private/GeometryCacheStreamingManager.h
Gets a pointer to a chunk of cached geometry data. Can be called from any thread.
Either the desired chunk or NULL if it's not loaded
const uint8 * MapChunk ( const [UGeometryCacheTrackStreamable](API\Plugins\GeometryCache\UGeometryCacheTrackStreamable) * Track, uint32 ChunkIndex, uint32 * OutChunkSize )